AndrewPlanckfirstcametomyattentionwhenhesubmittedtoLunarPhotooftheDayanimageofthelunarcraterPitatusandaphotoofapiehehadmade.Boththe60-milediametercraterandthe10”widepieareringedbyfracturesthatprobablyformedthesameway.Gasesassociatedwiththelavasthatfilledthecraterlifteditsfloor,whichcooledandthencollapsedwiththefracturesmarkingthebreakingpoint.Thepiecrustdidthesame,withthegasescomingfromcherriesratherthanlavas.Althoughthepieislonggone,youwillalwaysthinkofitwhenobservingPitatus.This comparison is characteristic of Andrew’s practical approach to observing andunderstanding the Moon. His new observing guide, What’s Hot on the Moon Tonight?,pointsoutinterestingtargetstoobserve,nightbynightduringthelunarmonth.Therearedescriptions of the craters, mountains, rilles and domes that you can see, but also briefexplanations of the geologic processes that formed them. Understanding what you seemakesobservingfarmoreinteresting—ithascertainlyhookedmeformorethan50years.Likethetitle,thewritinginWhat’sHotontheMoonTonight?isbriskandfun.Becausemanyunfamiliartermsareneededtodescribelunarfeatures,Andrewincludesa35-pageGlossary,whichisreallyamisnomer.Ratherthanbeingsimplyadrudgeofdefinitions,itisaseriesofmini-essays.What’sHotalsoincludes12pagestellingalittleaboutsomeoftheancientandmodernscientistswhosenameshavebeengiventolunarfeatures.Youwilllearn,forexample,thatthemonkwhoaddedthenameCopernicustotheMoondiditasaninsult by flinging the then controversial scientist’s crater into the Ocean of Storms. Themonkisforgotten,thefameofCopernicusiseternal.ReadingabouttheMoonisfine,butAndrewalsoencouragesyoutomakenotesfromyourobservationsbyprovidingplentyofspacetowritedownyourobservations,aswellascircularformssoyoucansketchwhatappearsintheeyepiece.Beingforcedtofillinablankspaceonadrawingdrivesyoubacktotheeyepiecetolookmorecarefullyateverypieceofthelandscape,therebyincreasingyourfamiliarityandknowledge.What are you waiting for? Grab your telescope, a pencil and this book for a personaltourofthemagicalworldinoursky.CharlesWoodAuthorofTheModernMoon:APersonalViewCreatorofLunarPhotooftheDay,LPOD.wikispaces.com

Acknowledgments

Firstandforemost,Iwouldliketothankmywife,Susan,whogivesmeinspirationtodocreative things. She patiently supported and encouraged me through the several years ittooktowritethisbook.Susanalsoreadtheentiremanuscript,redpencilinhand,andwitha wife’s unfailing instinct helped keep me subdued when I was tempted to stray duringunbridledmoments.OnedayIserendipitouslystumbledintoamonthlywriters’groupthatwasconductedbyJudithBriles(TheBookShepherd)inherhomeinAurora,Colorado.Judithhasastunningamount of knowledge about writing and publishing and shares it freely at her monthlymeet-ups.Iwasdoublyfortunateinthatherhusband,JohnMaling(EditingByJohn)isagifted professional editor and I promptly hired him to edit this book. I am enormouslygratefultohimfortheworkhedid.JudithandJohnrecommendedtheirfriendandcolleagueNickZelinger(NZGraphics)todothebookdesign.IamequallyindebtedtoNickforthesuperiorworkhedidforthecoverandinteriordesign.Iwouldliketothankmyfriend,SallieGreenwood,whoisawriterandeditor,forverykindlyagreeingtolookoverthemanuscriptandmakecomments.My long time astronomy buddy, Andy Robertson, also read the manuscript andcorrectedseveralglaringerrors.I am indebted to Charles Wood, author of The Modern Moon: A Personal View, forwritingtheForeword,andalongwithWesHiggins,givingmepermissiontousethephotoof the crater Pitatus which was published on the Lunar Photo of the Day website forMarch10,2006(LPOD.wikispaces.com)MyfriendBrianKimballoftheLongmontAstronomicalSociety(anastro-photographerparexcellence)allowedmetouseseveralofhisphotos.DanaThompsonoftheColumbusAstronomicalSocietygavemepermissiontousehisphotooftheLunarX,alittleknownphenomenonwhichappearsonlyforafewhoursonlunarDay6.I am indebted to Mike Siddoway, professor of mathematics at Colorado College, forworkingouttheformulaforpersonaleyeresolutionfoundintheGlossary.Gray Photography of Corpus Christi, Texas, kindly provided the photo used in the“AbouttheAuthor”sectionfreeofcharge.Unless otherwise noted, all other images are from NASA / USGS / BMDO / LROC /ASU/DLR/LOLA/MoonGlobe.Usedbypermission.

HowtoUsethisGuide

TheMoongetsabadrap.Althoughitisathingofastonishingbeautyandcomplexity,itis often looked upon by astronomers as a benevolent nuisance. It’s great for poets andlovers, but it interferes with the viewing of faint fuzzy things that are millions of lightyearsaway.BecausethefeeblelightfromtheseobjectsiswashedoutbytheMoon’sglare,astronomers will frequently not even bother to take out their telescopes when there is aMoon in the sky. In doing so, they deprive themselves of one of the richest and mostfascinatingviewsintheentireheavens.Paradoxically,ifwecouldseeJupiter,Mars,andSaturn in the same detail that we see the Moon, we probably would never leave ourtelescopes!One of the main purposes of this guide is to encourage astronomers to look upon theMoonasafriendinsteadofanadversary.Itisdesignedtoenabletheobservertositathis––––Thereareroughly300,000craterswiderthan0.6milesonthenearsideoftheMoon.––––––––orhertelescope,turntoaparticulardayinthelunarmonth,andspendsubstantialtime“walking”overthelunarsurfaceobserving,exploring,readingabout,andunderstandingthe history and formative processes of its various features. Both beginners andexperiencedastronomerswillfindthisguidetobeenormouslyuseful.The Moon is a delightful playground that will keep you fascinated for many years.Althoughsome10,000craterslargerthantwomilesindiameterarevisiblethrough––––Someearly60mmtelescopeshadgottensomeundeservedbadpress.Myfirsttelescopewasa60mmTasco.Althoughithadasmallaperture,onceIinvestedinhighqualityeyepiecesthetelescopeperformedadmirablyandgaveperfectdiffractionpatternsaroundstars.FiftyyearsandsixtelescopeslaterIstillhave(anduse)thatTasco!––––––––amateurtelescopeswithatleasta6”aperture,thisguideisnotmerelyalistofobjects;itisdesignedtoincreaseyourenjoymentbyincreasingyourunderstanding.Itwillteachyouhowto“read”theMoonasyouarestrollingaboutitssurfacewithyourtelescope.Evenasmall 60mm telescope will show you an astonishing amount of detail. Take your time;don’tbeinahurry.Thisisanopportunitytostopandsmelltheroses.In addition to a telescope and this book, you will need a good map of the Moon(preferablySky&Telescope’sFieldMapoftheMoonavailablefromskyandtelescope.comoramazon.com).TheFieldMapisthefinestmapoftheMoonavailableandisdesignedtobe used comfortably at the telescope. Lunar features that are described in this book arekeyed to Sky and Tel’s map, and entries will look like this—Plato: [NW/D9; L=9°]—

meaningfoldyourFieldMaptothenorthwestquadrant,gridlocationD9.1However,anymapthathasthefeaturesindexedwillwork.TheentryL=9°indicatesthelongitudeofthelunarfeatureandcanbeenormouslyhelpful.Whenyouareplanninganight’sobservation,findoutwhatthelongitudeoftheterminatorwillbe(youcanusetheMoonMapProappfor this).2 Any lunar feature which is within 10° or so of the terminator will haveastonishingdetail!Manyofthefeaturesdescribedareaccompaniedbythumbnailimagestohelpyougetoriented. I have deliberately kept these images small, as this should be a voyage ofpersonaldiscovery.Yourmostexcitingmomentswillcomewhileyouareattheeyepiece,notwhileyouarelookingatpictures.If you have a smartphone or similar device, then take advantage of the severalastronomyappsthatareavailableoniTunessuchasSkySafari,LunarPhase,MoonMapPro,andMoonGlobeHD.3 As of this writing, only SkySafari will give you the criticalLunarDayfortheeveningthatyouplanto––––TheMoontakesabout29days(fromnewMoontonewMoon)tocyclethroughitsphases.ThesearereferredtoasLunarDays1-29.So,forexample,ifyouwishtoobservetheMoonatfirstquarteryouwouldturntoDay7inthisguide.––––––––doyourobserving.Curiously,MoonMapProistheonlyappthatgivesthelongitudeoftheterminator,apieceofinformationthatwillbeenormouslyhelpfultoyouasyouusethisbook.TheMoonGlobeHDapprenderstheMoonwithmind-bogglingclarity!Withityou will be able to zoom in on even the smallest craters without losing detail. (At fullzoomyoucanseecratersthatareassmallasonearc-second—theequivalentofviewingtheMoonataround250x.)Observing the Moon has several advantages over traditional astronomy, chief amongwhich is that you can observe the Moon from the middle of a city through the worst oflightpollution.Andsinceyouwillbespendingsubstantialtimestaringatabrightobject,youmaydispensewiththeobligatoryredlight.4Useawhiteflashlighttoconsultthis––––Ittakesupto30minutesforyoureyestobecomedarkadaptedenoughtoallowyoutoseeveryfaintobjects.Acarelessburstofwhitelightwilldestroythisinaninstant,butredlightwillpreserveyournightvision.––––––––book and make notes. No more squinting is one of the many pleasant benefits ofstudyingtheMoon!Youcanalsobeginyourobservingduringthebrighterportionsoftwilight,beforeanystarsarevisible.TheMooncanevenbeobservedprofitablyduringthedaytime.Thelunarobservercanusuallygettobedatadecenthour.

The Glossary at the end is a great deal more than a simple definition of terms. Itcontains all the information you will need to get a basic understanding of the Moon: itsformativeprocesses,itshistory,howitcametobe,thedetailsofcraterformationandoftheotherfeaturesthatyouwillbeobserving.ArewardingcloudynightactivitywouldbetositdownandreadthroughtheentireGlossary.TermsthatareinboldfacearecoveredintheGlossary.What’s Hot on the Moon Tonight? begins on Day 1 of the lunar cycle (New Moon isessentiallyDay0)andproceedsthroughFullMoon.Withsomeexceptions,thedaysafterFullMoonarenotincludedbecausetheseobjectshavebeencoveredearlier(e.g.,objectsneartheterminator on Day 17 are the same objects that were covered on Day 3). Theonlydifferenceisthattheterminatorisontheothersideofthesefeatures,andsunlightisstreaminginfromtheoppositedirection.Soifyoufind,forexample,thattheMoonforDay3istoolowonthehorizontoseeobjectsclearly,waituntilDay17or18whentheeveningterminatorwillbeinaboutthesameposition.ImmediatelyfollowingeachDayentryyouwillfindaterminatornumber(T-number),whichindicatestheapproximatelongitudeoftheterminator.FeaturesontheMoonlookquite dramatic when they are within 10° or so of this line. However, the T-numberassumesthattheMoonhasnolibration(theapparentrockingbackandforthoftheMoon)so,dependingonthedegreeoflibration,theactuallongitudeoftheterminatoronthenightyouareobservingmayvarybyupto7°fromtheT-numberthatislisted.AlsokeepinmindthattheterminatorcreepsacrosstheMoonatapproximately10milesperhour(whichcorrespondsroughlyto9arc-secondsatthemeandistanceoftheMoon).Accordingly,youmightwishtogoforwardorbackwardinthebookby––––Acircleisdividedinto360°.Adegreeisdividedinto60arc-minutes,andonearc-minuteequals60arc-seconds.(Thisisprettysmallstuff—apinheadat100yardssubtendsanangleofonearc-second.)Alow-powereyepiecewilltypicallyshowmorethan30arc-minutes(thewidthoftheFullMoon).––––––––oneday.(TheMoonMapProappwilltellyouexactlywheretheterminatorisontheeveningyouplantoobserve.)Ihavemadenoattempttolistalloftheobjectsthatarevisibleonaparticularlunarday;the observer would be overwhelmed by uninteresting minutia and this guide wouldquicklyloseitsvalue.Inaword(averysubjectiveword)ifobjectsarelisted,itisbecauseI have found them interesting to look at, or there are unusual formative processesinvolved, or they have a story to be told. In many cases it will be a combination of allthesethings.Althoughthemostpertinentinformationhasbeenincludedinthetextproper,ancillaryinformation will be diverted to footnotes, sidebars, the Glossary, and the appendices sothatyouwon’tbedistractedfromtheenjoymentofviewing.BecausemanyofthefeaturesontheMoonhavebeennamedafterindividualswhohavechangedthecourseofhistory,

by the time you have finished observing for one lunar month and read all the attendantinformation, you will have, in effect, completed a mini-course in Western civilization.Craterswhicharenamedaftersuchpersonshaveasmallsymbolfollowingtheirnames,such as Aristarchus:† This symbol directs you to Appendix A: Historical Notes whereyoucanreadaboutthecontributionsthesepeoplehavemade.Asisthecasewithobservingdeep-skyobjects,themoreyoulook,themoreyousee.Tothisend,inthehardcopyversionofthisbookeachfacingpageisablanksheetwithlinesprovidedtomakenotes,dodrawings,andencourageyoutoreallylook.(Ifyourunoutofspace, there are extra blank pages provided at the end of the book plus an additionalsectionconsistingonlyofblankdrawingcircles.)Ifyou’relikemostpeople,theideaof“doing drawings” is an intimidating prospect. You probably don’t bother because youthinkyouhavenotalentandyou’dratherspendyourtimeobservingthantryingtofinesseyourineptsquigglesintosomethingyourgrandmawouldbeproudof.Here’s the secret: Forget grandma—you’re going for quick lines, circles and dots,nothing more! Spend no more than two minutes drawing a crater and its prominentfeatures.Theideaistoquicklyrecordwhatyoucansee,thencomebacklaterandtrytosee more. Don’t be surprised if, after a few sessions, you discover that you’re lookingforwardtonightsthataredominatedbytheMoon.As you are planning a night’s observation, it would be a good idea to read over thecorrespondinginformationfortheLunarDayinquestionbeforehandsothatyouhaveanidea of what to look forward to. This would be particularly helpful if you are doing apublicstarparty,asyouwillbepreparedtospeakknowledgeablyaboutfeaturesthatwillbeprominentthatevening.Inanycase,thenexttimeyousitdownatyourtelescope,openthisguideandreadabouttheobjectsyouareobserving.Don’tbeinahurry.Takethetimetosavorandenjoywhatyouarelookingat.Happyviewing!

The Moon observer should be familiar with the names and positions of the 10 majorseas: Crisium, Fecunditatis, Nectaris, Tranquillitatis, Serenitatis, Frigoris, Imbrium,Nubium,Humorum,andOceanusProcellarum.(Thisisakintofindingyourwayaroundtheskybyknowingtheconstellations.)

NightlyGuidetoLunarFeatures

DAYS1&2(T=79°-68°E)5

BecausetheMoonissoverylowonthehorizon,Days1and2arereallynotworththetrouble.WaituntilthefirsttwodaysafterFullMoonwhenyoucanseethesefeaturestogreateradvantage.However,someastronomersplayagameoftryingtospotthe––––WithinIslamiccultures,spottingtheearliestMoonisnotagamebutquiteaseriouspartoftheirreligion,asmanyoftheirpracticescannotbeginuntilthefirstsliverofacrescentMoonhasbeensighted.––––––––earliest possible Moon with the naked eye. The best time to view such a Moon is inMarchandAprilbecausetheecliptic(theapparentpathoftheSunandplanetsagainstthestarrybackground)ismoreperpendiculartothehorizon.Asaresult,aftertheSunsets,acloselytrailingMoonwillbecomevisibleinadarkskymorequicklythanatothertimesinthe year. After the Sun has set and twilight has begun, scan the area around the sunsetpointonthehorizonfortheMoon.DonotattemptthiswithbinocularsuntiltheSunhascompletelyset.Permanenteyedamagewillresultifyouaccidentallyviewthesunthroughbinoculars!Humboldt: [SE/M18; L=81°E] This crater is best viewed when there is a pronouncedlibration.Becauseofforeshortening,itappearstobeextremelyelongatednorthtosouth.Ithas a cluster of central peaks, and if you’re lucky you might spot a long catena (craterchain)extendingfromthenortheastrimofthecrater.PromontoriumAgarum:[NE/H16;L=66°E]animpressivecapeontheSEedgeofMare––––LTP’sareshort-livedchangesinlightingorcolor(eithersuddenorgradual).

Theymanifestthemselvesasobscurations,foggypatches,etc.––––––––Crisium. It has peaks which rise to several thousand feet above its floor. LunarTransientPhenomena(LTP’s)haveoccasionallybeenreportedinthisregion,especiallyrightaftersunrise.

OneoftheloveliestviewsoftheMooncanbeseenaroundDay3,andtoappreciateityou don’t even need a telescope. Go out in the evening of the third day, just as deeptwilight is ending, and look west. The Moon will seem magically suspended over thehorizon, and its dark side will be softly glowing from earthshine.6 At such times thedaylightportionoftheEarthshinesabeaconofreflectedsunlighttowardtheMoonwhosedarksideacquiresalovelyetherealglow.Weperceivethisglowasearthshine.Springisan especially good time to enjoy this sight. It is particularly lovely when Venus issuspendedjustnexttotheMoon,andifyoucanpossiblyaddthearomaofnearbyappleblossoms then you will have created a scene of transcendental beauty. It is a time forloversandpoets.TheGreatEasternChain:[SE/K-N16;L=61°E]Thereisaconspicuouschainoflargecraters,atonetimereferredtoastheGreatWesternChain,whichcloselyhugsthesame

meridianneartheeasternlimb(i.e.,therimofthevisibledisk)oftheMoon.TheystartonthesoutheasternshoreoftheSeaofFertilityandcontinuesouth7.ThechainconsistsofLangrenus,Vendelinus,Petavius,andFurnerius.Thesecratersstartedtocomeintoviewlastnight.Althoughthisunusualalignmentiscoincidental,itwasoncepositedasevidencetosupporttheendogenictheoryofcraterformation—thenowdisproventheorythatthemajority of craters were formed by volcanic forces originating from within the Moon.(ComebackonDay17whenyou’llbeabletoseethemmoreclearly.)Langrenus&Vendelinus:[SE/K-L16;L=61°E]ThesecratersarethefirsttwosegmentsoftheGreatEasternChain.LangrenusandVendelinusaretwolarge90-mi.craterslocatedonthesoutheastshoreofFertility.Oneisconsiderablyolderthantheotherandappearedbefore the lava flows started. It should be easy for you to decide which is which.8 TheterracesandcentralpeaksofLangrenuswillhaveemergedfromlastnight’sshadows,andtonight the crater is a beautiful sight. Even if you have a small telescope, there is muchdetailintheinteriorandontheouterrampartstokeepyoubusy.Becausetheappearanceofthecraterchangessignificantlywithdifferentlightingangles,makesomedrawingsofwhatitlooksliketonightandcomebackoverthenextfewnightstocomparetheviews.TheyoungercraterLaméintrudesonVendelinusonitsNErim,anditisappropriatelysmaller.However,noticethatLamé,inturn,overlapstwosmallerunnamedcratersonitsSWrim.Thisisunusualinthatintrudingcratersarealmostalwayssmallerthanthecraterstheyimpacton.Petavius:[SE/M16;L=60°E]ThisisoneofthemostbeautifulcratersontheMoon,butitmaybemoreprofitablyseenonDay17whentheMoonisnotsolowonthehorizon.Itis

anexampleofafloor-fracturedcrater(FFC),atypeofcraterthathasbeenmodifiedbylatervolcanism,uplift,andconsequentfracturing.Becauseofthecurvatureofthelunarsurface, the floor of Petavius is nearly 1,000 feet higher near its center than around theedge! Is the curvature apparent to you? Turbulence and volcanic upheaval from belowsplitthecentralmountain(whichrisestonearlyonemileabovethefloor)andformedtherilles.Theprincipalrilleonthefloor,RimaPetavius,issoprominentthatitcanbeseenwitha60mmrefractor.9Itisagraben,anelongateddepressionthatresultswhenstressesopenuptwoparallelcracksinthelunarcrustandtheterraininbetweendrops.Therilleextendsfromthecentralpeaktothesouthwestwall.Thereareactuallyseveralrillesonthefloor.Makeadrawingofhowmanyyoucanseewithyourinstrument.Furnerius: [SE/N16; L=61°E] This is the last of the craters that make up the GreatEasternChainanditisveryold,havingformedbeforetheimpactthatcreatedtheNectarisbasin

3.9billionyearsago.Althoughthewallshavebeenbattereddownandshowtheirage,therearestillmanycomplexitiesremainingwhichwillrewardcarefulobservation.ThereareseveralcraterletsofvaryingsizesonthefloorofFurnerius,includinga30-milerilleextendingfromthenorthrimtowardthesoutheast.PatrickMoorereportsthattherearefourteenlargecratersandseveralcraterletsinitsinterior.(Amorereasonableassessmentwould be there is one large crater and several craterlets.) Make a rough sketch of howmanyyoucansee,thencomebacknextmonth(andonDay17)toseeifyoucanaddtothecount.CanyoumatchPatrickMoore’sobservingskills?MareCrisium:[NE/H15;L=59°E]OnDay3theSeaofCrises,thefirstofthelargeseastobecomevisibleonthewaxingMoon,hasnowbeenfullyrevealed.Wetendtothinkof

cratersascomparativelysmallobjectsandlosesightofthefactthatlargelunar“seas”are the result of crater impacts also. Basically, if it’s round, it’s a crater. Mare Crisiumresultedfromtheimpactofalargemeteor3.9billionyearsago.Theeventwasenergeticenough to leave a multi-ring imprint, parts of which we can clearly see. Notice the ringfeaturesbendingaroundCrisiumonitsnorthside.ParticularlynoticehowMareAnguisontheNEsideofCrisium[G16]extendsitselftowardthewest,passesbelowCleomedes,and then dissipates at Tisserand. The Crisium basin appears elliptical, with its long axisrunningfromnorthtosouth.Thisisanillusionduetotheeffectsofforeshortening.Crisiumactuallyiselliptical,but,contrarytowhatyoureyestellyou,itslongaxisrunseasttowest.TakeamentalimageofhowmuchspacethereisbetweenMareCrisiumandthe––––IfyouhavetheMoonGlobeHDapp,youcanseetheeffectsofforeshorteningforyourself.DoasearchforMareCrisiumasitnormallyappearsneartheeastlimboftheMoon.Noticehowitiselongatednorthtosouth.Thenwithonefinger,moveCrisiumtothecenterofthescreenanditwilldevelopitstrueeast-westelongation.––––––––easternrimofthelunardisk.Thiswillvaryfrommonthtomonth,evenfromnighttonight,andwillbeanindicatorofhowmuchlibrationhascomeintoplay.Once you have become familiar with the details on the surface of Mare Crisium,

particularlyaroundPromontoriumAgarum,beonthelookoutforLTP’s.Thesehavebeenreportedfromtimetotimeandmanifestthemselvesasmiststhatmysteriouslyappearandobscuresomeofthesurroundingdetails.Endymion:[NE/D15;L=57°E]ThisisanoldercraterwhichsomewhatresemblesPlato[Day 8; NW/D9] in that it has a smooth, dark-chocolate floor and three-mile-high wallswhichcastlovelyshadowspiresonthefloodplainbelowwhentheSunislow.Geminus:[NE/F15; 57°E] Roughly 200 miles north of Mare Crisium (above) you willfindthe––––200mileswouldbeaboutthreearc-minutesnorthofCrisium.Beingfamiliarwiththefieldofview(FOV)ofyoureyepieceswillhelpyounavigate.––––––––moderately complex 55-mile crater Geminus. It has terraced walls and small centralpeaks.Thiswillgiveyouanindicationofwhattostartlookingforinthefollowingdaysascratersbecomeincreasinglymorecomplex.Burckhardt:[NE/F15;L=57°E]Thisisthecraterwiththe“MickeyMouse”ears.Itisaremarkableexceptiontotherulethatwhenonecraterintrudesuponanother,theyoungercrater (the intruder) is always smaller. Burckhardt has landed smack in between twosmallerbutoldercraters,givingittheMickeyMouseeffect.Cleomedes:[NE/G15;L=56°E]CleomedesisthefirstsignificantcraterjustnorthofMareCrisium.Itisasplendidcrater,80milesindiameter,withterracedwalls,rilles,anda

small central mountain. There are also two craterlets, and a y-shaped rille on thenorthern half of the floor just east of the central mountain peak. Notice that the floor isunusuallysmooth.Becauseitssouthernrimtouchesoneofthemulti-ringsencirclingtheCrisium basin, it is believed that lava rose up through Crisium fractures and smoothly

coveredthefloorofCleomedes.Underalow-angleSunyoumightbeabletodetectthattherillecutsthroughasmalldomeonthenorthernsectionofthefloor.Aristarchus:† [NW/G5; L=47°W] The crater Aristarchus is the brightest spot on theMoon.ItissobrightthatSirWilliamHerschelmistookitforaneruptingvolcano,anditsglowcanevenbeseencomingthroughonthedarksideoftheMoonaroundDay3whenitisilluminatedonlybyearthshine.10Whileyou’reatit,seeifyoucanspotsegmentsoftheTychoraysystemwhicharealsovisibleunderearthshine.11

DorsumOppel:[NE/H15;L=53°E]AsthelavacooledfollowingtheimpactthatcreatedMare Crisium, a series of wrinkle ridges, known as Dorsum Oppel, formed along theentirewesternedgeandgivetheimpressionofwaveslappingontheshore.Theflowinglava partially filled the pre-existing craters Yerkes and Lick [H15], turning them intoghostcraters.ThereisalsoamoresubstantialridgethatconnectsthefloodedcraterYerkeswiththesmallerYerkesE,15milestoitsnorthwest(unnamedontheFieldMap).UnderalowSun,whentheterminatorisaround52°-55°,thisridgewillcombinewiththeSWrimofYerkesto look remarkably like the silhouette of a bird in flight. It has consequently beennicknamed the Flying Eagle. (This feature may be seen to better advantage on Day 18whentheSunissetting.)Peirce&Picard:[NE/H15;L=54°E]ThetwolargestintactcratersonMareCrisiumarePeirce and Picard. They are only about 12 miles in diameter by 1 mile deep and willrequire75x-100xtoseethem.Theyarelocatedonamoreorlessnorth-southlineabout30miles in from the western shore of Crisium (Peirce is the northernmost). The lava thatcoveredCrisiumstoppedflowingbeforethesecratersformed.YoushouldeasilybeabletospotSwift,asmallseven-mi.craterjusteightmilestothenorthofPeirce.VallisRheita:[SE/N14;L=52°E]At276miles,theRheitaValleyisthelongestdistinctvalley on the Moon. If you look closely at this formation, you will see that it is not avalleyin

Fertilityandcanbeeasilyseenthroughthesmallesttelescopes.Thecratershaveapairofsplashraysthatresemblethetailsofacomet(anappropriateresemblance,consideringwhotheyarenamedafter).Theserays,whichextendabout75milestothewest,haveahappycharacteristicinthattheyarevisibleunderloweranglesofillumination.Itisunusualtobeabletoseebothacraterandtheraysitproducedatthesametime.(SeeTychoonDay8[SW/P8],themostconspicuousexampleofsplashrays.)Themostcommonlyacceptedexplanationoftheoriginofthisunusualfeatureisthat––––CharlesMessierdiscoveredsomanycometsduringhiscareerthathewasdubbed“TheFerretofComets”byKingLouisXVofFrance.––––––––aprojectilecameinatalowangle(1°to5°)fromtheeast,smashedintotheMoontoexcavate Messier, and then ricocheted. When it landed the second time Messier A wasformed,alongwithitsattendant“comettails.”Theprojectile’sextremelylowangleof––––WhenIwasayoungsterandfirstobservedMessierandMessierA,thetwocraterswereknownasMessierandPickering.Iwasfascinatedbythepairandboughtintotheromanticnotion(whichwasbeingproposedatthetime)thattheformationrepresentedatunnelthathadbeenblastedthroughamountainrangebyalowflyingmeteor.Whenthecoldlightofmodernsciencerevealedthatthiswasnotthecase,Iwascrushed.(Ihavenotyetrecoveredfromthedisappointment.)––––––––approach explains the oblong shape of the craters. Notice that the Messier impact